ITQ-32 is a molecular sieve having a two-dimensional pore system comprising cages linked through windows of 8-membered rings of tetrahedrally coordinated atoms. Although the widest cross section of the large cages is circumscribed by 12-rings, these 12-rings can only be accessed by diffusion through the 8-ring channels. ITQ-32 has been assigned the framework type IHW by the Structure Commission of the International Zeolite Association.
ITQ-32 is of interest for the separation of small molecular species like carbon dioxide and methane because of the small dimensions of its pores (3.5 Å×4.3 Å). This and other separations using ITQ-32 are described in, for example, U.S. Patent Application Publication No. 2009/0202416.
The characteristic X-ray diffraction pattern of ITQ-32 and its synthesis in the presence of N,N,N′,N′-tetramethyldecahydrocyclobuta[1,2-c;3,4-c′]dipyrrolidinium and 4,4-dimethyl,1-cyclohexylpiperazinium cations as organic structure directing agents are disclosed in U.S. Pat. No. 7,582,278. However, the synthesis mixtures described in U.S. Pat. No. 7,582,278 require the presence of fluoride ions, which in commercial scale operations is disadvantageous in that they may lead to extra safety and cost considerations. There is, therefore, interest in synthesizing ITQ-32 in the absence of fluoride ions.
According to the present invention, it has now been found that ITQ-32, particularly in a borosilicate form, can be prepared in the absence of fluoride. The fluoride-free synthesis can be effected using 4,4-dimethyl,1-cyclohexylpiperazinium as the organic structure directing agent. The synthesis can be accomplished in the absence of alkali metal cations thereby obviating the need for ion-exchange of the product after calcination to remove the occluded organic structure directing agent.